The invention relates to biomedical devices for quantitative measurement and analysis of progressive loss or recovery of motor activity in human subjects.
Diseases such as stroke, amyotrophic lateral sclerosis (ALS), and Parkinson's disease frequently result in motor deficit. It would be useful for medical personnel attending to victims of these diseases to have available a straightforward and quantitative measurement of the extent of motor deficit. Such a test would, for example, allow assessment of stroke severity, which would in turn assist in the development of standardized protocols for treatment keyed to severity. Furthermore, ongoing research toward the development of palliative drugs necessitates accurate assessment of the progress achieved by these drugs. Several methods have been developed for these measurements.
Following stroke, subjective criteria are frequently used in the measurement of motor function. In one such test, a subject curls his or her fingers and attempts to resist an examiner's attempt to straighten them. Inability by the examiner to uncurl the fingers is scored as 5+ on the Medical Research Council's 0 to 5+ scale; mild weakness is 4+, action against gravity but no other external force is 3+, and so forth down to 0, equaling no resistance from the subject. However, such studies have been shown to be irreproducible and the results are often ambiguous.
Other tests, including evaluations of grip strength and finger tapping ability, provide more useful measurements in the assessment of stroke severity. For example, a spring-based dynamometer with a mechanical needle gauge can be used to measure the force with which the subject can squeeze (Spreen et al. "A Compendium of Neuropsychological Tests", 1991, pp. 367-373; Trombly Occupational Therapy for Physical Dysfunction, 1995, p. 151; Kellor et al. Am. J. Occup. Ther., 1971, Vol. XXV, No. 2, pp. 77-83; Heller et al. J. Neurol., Neurosurg., and Psych., 1987, Vol. 50, pp. 714-719). Electrical dynamometers have also been developed with the capability of recording maximal grip strength (contraction amplitude) or the time between the initiation of contraction and the peak contraction amplitude (contraction time).
Finger tapping ability has been tested with devices ranging from mechanical tallying units (Heller et al. J. Neurol., Neurosurg., and Psych., 1987, Vol. 50, pp. 714-719; Spreen et al. "A Compendium of Neuropsychological Tests", 1991, pp. 367-373) to video surveillance systems that capture minute finger tremors (Frischer Neuropsychologia, 1989, Vol. 27, No. 10, pp. 1261-1266). Still other devices include electrical counters capable of calculating tapping frequency and interval between taps, and the mean, standard deviation, and coefficient of variation for these quantities (Shimoyama et al. Arch. Neurol., 1990, Vol. 47, pp. 681-684).
Two scales are widely used in the evaluation of neurological status following stroke. The NIH stroke scale includes numerous components, such as assessment of language ability, vision, sensory function, level of consciousness, and motor function. The Fugl-Meyer scale assesses sensory motor function after stroke. A Fugl-Meyer arm motor subscore can also be employed; this subscore examines a multitude of factors, including deep tendon reflexes, synkinesia, strength, dexterity, tremor, and coordination.
Assessment by these traditional methods (i.e., NIH or Fugl-Meyer) is burdened by several considerations. First, excellent interobserver agreement is achieved only with extensive training. Second, the tests are time consuming, requiring about 15 minutes or longer per test for an experienced analyst. These two issues have increased in importance in recent years due to the proliferation of new drug trials.